| Restraining the decline of submerged macrophyte communities and accelerating the restoration and reconstruction of the submerged macrophytes are the key links to iaprove the ecological environment of Baiyangdian Lake.Based on ecological water supplement to the Lake,this paper explored the distributio n characteristics of submerged macrophytes in Baiyangdian Lake.The effects of water level on the growth status and water purification efficiency of Vallisneria spiralis(indigenous species)were systematically investigated by field simulation experiments;effects of nitrogen loading and Carassius density on growth and water purification of Potamogeton crispus and Ceratophyllum demersum L.A scheme for the construction of submerged plants in water restoration area was proposed.The main achievements are as follows:Pollution-tolerant species populating and indigenous species declining are the general characteristics of submerged macrophytes in Baiyangdian Lake.Based on the investigation results of water depth,water quality and submerged macrophytes in 8 monitoring sections of Baiyangdian Lake in Summer and Autumn,water level and water quality are the key factors affecting the distribution of submerged macrophytes community.The water depth of the monitoring points in Duancun,Wangjiazhai,Quantou,Shaochedian and Nanliuzhuang ranges from 2.01 to 3.28 m.Water quality is inferior in Class V according to the limits of water quality of surface waterbody.TN is the main factor exceeded the standard,ranging from 1.91 to 5.94 mg/L.Contamination-tolerant species,such as Ceratophyllum demersum L,Potamogeton crispus and Euphorbia longifolia,are the main submerged macrophytes.Only little amount of Vallisneria spiralis(indigenous species)is located.While the water depth of the monitoring points in Caiputai,Guangdianzhangzhuang and Zaolinzhuang ranges from 1.67 to 2.35 m,and the water quality is generally accordance with Class IV TN(0.41-1.74 mg/L)and TP(0.027-0.059 mg/L)are the main exceeding factors.Myriophyllum spicatum L.and Hydrilla Rich are the main submerged macrophytes.As an indigenous and once dominant species,the distribution of Vallisneria spiralis is limited,meanwhile,the trend of dec lining is obvious as a whole.Water level plays an important role in the growth of Vallisneria spiralis(indigenous species)and in its water purification performance.Within the range of 40-160 cm,the relative growth rate of Vallisneria spiralis increased with the water deep first and then decreased,and the maximum result of 2.02 mg/g/d was reached at 120 cm.The total removal rates of TN,TP,NH4 +-N and COD reached 72%,58%,96%and 74%,respectively.The concentration of TN affected the growth and water purification performance of Potamogeton crispus and Ceratophyllum demersum L.The growth of Ceratophyllum demersum L was better than that of Potamogeton crispus at TN 4.50 rng/L,meanwhile,the removal efficiency of TN,NH4+-N and TP by Ceratophyllum demersum L was significantly higher than that ofby Potamo getoncrispus.Under the condition of the growth of Potamogeton crispus was better than that of Ceratophyllum demersum L at TN 1.25 mg/L,but the removal efficiency of the two plants was similar.With the increase of the density of crucian carp,the negative effect on water quality was strengthened.Finally,a reconstructed strategy of the submerged macrophytes in Baiyangdian Lake is proposed The water depth of lake restoration area can reach 40-160 cm,used cuttage to plant Vallisneria spiralis;The water depth in mild eutrophication area is about 3 m,on the basis of the existing submerged macrophytes,suitable addition of Ceratophyllum demersum L and Potamogeton crispus that can withstand deep water environment can be made,planting by cuttaging and sowing;The water depth in moderate and severe eutrophic areas can reach about 3 m.should be put on the prevention of companion species(Potamogeton pectinatus L and Charophyceae).planting by cuttaging and Sinking method.The density of crucian carp in each lake area should be less than 0.2±0.03 g/L. |
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